Embodiments of the present invention relate generally to frequency generation, synthesis, and processing.
Modern communications equipment design relies on the generation of various periodic output frequencies. While oscillators are preferred for their overall stability and purity, individual oscillators differ, and the issues of amplitude stability and spectral purity are ever-present. Moreover, while stable oscillators built with high-Q crystals often exhibit excellent spectral purity, such oscillators can usually only be tuned over a range of several hundred parts per million. Since most communications equipment must operate at a number of different frequencies spanning a considerably larger range, and because it is usually not economical to fabricate separate oscillators for each frequency to be generated, frequency synthesizers are widely used in modern communications circuit design. Given their advantages, synthesizers are thus often used as the core of multi-channel communications circuit design. However, the low-pass control loop filters used in phase-locked loop (PLL)-based synthesizers often require a large resistance-capacitance (RC) time constant (which implies large values of resistance and capacitance) to provide proper control signals for the voltage-controlled oscillator (VCO) which is also part of the PLL circuit. These loop filters thus require large amounts of circuit surface area and power to operate.
The ability to provide many channels for communication, along with full usage of individual channel capacity, is often a major goal for the communications circuit designer. More and more channels are required to support the public demand for instant contact with others as the use of personal communications devices becomes more popular. Those skilled in the art also know that the capability to effect multi-channel communications provides a robust and scalable mechanism for circuit designs to achieve the goal of effectively utilizing all available channels. Increasing the data transmission rate may serve to enlarge the number of channels and increase bandwidth availability. On the other hand, the occurrence of one or more notches within a band of frequencies or even within a single communications channel (perhaps caused by destructive interference, resonant inter-circuit connectors, etc.) can reduce the availability of channels.
Conventional discrete time domain-based design approaches do not lend themselves to high data rate communications. And, as mentioned above, circuit designers are also concerned with the amount of circuit real estate and power required by conventional PLL-based multi-frequency solutions. Thus, there is a need in the art to increase the number of channels available for stable, low-jitter communication, along with reducing dependence on conventional high-area, high-power designs.